<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>这个不懂</title>
    <style>
        div{
            width:100px;
            height: 100px;
            background: red;
            margin-top:100px;
            padding-left:20px;
            border:100px solid #333;
            /* box-sizing:content-box(默认)|border-box给border，padding不会改变他的width,height */
            box-sizing:border-box;
            /* box-sizing:content-box; */
        }
        
    </style>
</head>
<body>
    <div></div>
</body>
</html>